It is known to coat fabric with protective coating systems containing water repellent chemicals and flame retardant chemicals to make the fabric suitable for use as military tenting in all climates of the world. See, for example, U.S. Pat. Nos. 4,594,286 and 4,833,006.
It is, of course, desirable in most climates that the tent fabric also be insect repellent. Insect repellents are known but their effective life of only a few days renders them unsuitable for use in a protective coating system for tent fabrics.
There is, therefore, a universal need for tent, tarpaulin, and shelter fabrics (collectively referred to herein as tent fabrics) which have a long term capability of repelling annoying and disease carrying insects.
Many insect repellents are effective when they are applied to the skin as a spray or lotion, but only for a few hours. The protection time is extended to as much as a week or ten days when repellents are applied to clothing, gloves and body nets for outdoor use. Insect repellents with such a short effective life are impractical for use in a coating for tent fabric.
The tent fabrics with which this invention is concerned are treated to be durably water repellent and flame retardant, and to have an appearance that is pleasing to the eye. In order that these properties be retained, it is necessary that the fabric be treated with insect repellents that are effective for their intended purpose without adversely affecting any other desired property of the fabric.
Several commonly known insecticides have been tried with the coating used for tent fabric. For example, a production trial has been made of water repellent and flame retardant tent fabric utilizing dimethyl pthtalate (DMP) as an insecticide. It did not compromise the flame retardant or water repellent properties of the tent fabric but its length of effectiveness was less than desired.
Benzil benzoate, while readily dispersed in typical fire retardant coatings, demonstrated an unsightly appearance upon application and drying. Dibutyl phthalate and dibutyl adipate showed this to a much lesser extent.
Permethrin is a synthetic pyrethroid which exhibits repellent as well as knockdown and kill activity against insects. Pyrethroids, including both the naturally occurring compounds and their synthetically prepared analogs effectively control a variety of pests, such as houseflies, mosquitoes, cockroaches, etc. They are not harmful to plants, food, animals and humans, and leave no harmful residues. Permethrin is environmentally safe and has been found to be compatible with coating compositions containing water repellent chemicals and flame retardant chemicals, used for tent fabric, without adversely affecting the desired properties of the coated fabric.
Despite these highly favorable characteristics, permethrin has had only limited general utility because of its relatively short-lived insecticidal activity. This is due to its decomposition into a non-active, non-insecticidal product in the presence of oxygen and ultraviolet light. The speed of this decomposition is dependent upon the environment in which the permethrin is placed, but typically takes place in from several hours to several days or weeks. This instability of permethrin severely limits its usefulness as an insecticide.
Prior attempts to stabilize pyrethroids against degradation have included encapsulation and the addition of antioxidants and photostable ultraviolet light absorbent compounds to solutions of pyrethroids. Encapsulation has not been effective because the pyrethroids degrade almost as quickly inside the capsules as they do unencapsulated. Only moderate success in reducing degradation has been obtained by the addition of antioxidants and photostable ultraviolet light absorbent compounds to solutions of pyrethroids. Their moderate success is largely off-set by unsightly residues which are hard to remove.
Various techniques have been suggested for providing sustained release of a pyrethroid as an insect control agent. For example, U.S. Pat. No. 4,056,610 to Barber discloses a microcapsule insecticide composition in which a pyrethroid permeates a porous shell wall and maintains an effective level of the pyrethroid upon the outer surface of the shell wall to control insects for up to four days (then considered an extended length of time within the art). Control is achieved by killing insects which contact the pyrethroid released through the capsule wall.
U.S. Pat. No. 4,765,982 to Ronning discloses an insect control device comprising a plurality of rough surfaced cellulosic fibers wherein there is self-adhered to the surface of the fibers a liquid insecticide composition microencapsulated in a capsule whose shell is permeable to the liquid insecticide. The microencapsulated insect control agents disclosed in U.S. Pat. No. 4,056,610 to Barber are named as the preferred insecticide for use in Ronning's invention.
Ronning's insecticide-treated-rough-surfaced cellulosic fibers are formed into webs, tapes, sheets, pads, and various other relatively flat shapes suitable for use in particular locations, such as a ribbon-like tape for placement along the base of a building or door.
Ronning teaches that smooth-surfaced fibers do not act as good sites for adhesion of microencapsulated insect control agents. Ronning's rough surfaced cellulosic fibers treated with an insecticide are not suitable for a tent fabric. The texture of the rough surfaced fibers is not satisfactory and they are neither water repellent or flame retardant.